1. Field of the Invention
This invention relates to an improvement in a service brake actuator for air-operated vehicle brakes; and, more particularly, to a service brake actuator having a unitary pushrod assembly with a separable bushing capable of being assembled about the pushrod for sealing the pushrod with respect to the service brake actuator.
2. Related Art
Air-operated brake actuators are well known in the vehicle industry, especially in the heavy-duty truck industry where the air-operated brake actuators are controlled by a source of pressurized air to apply the operational brakes and emergency brakes of the heavy-duty truck and/or trailer. A typical air-operated brake actuator comprises a spring brake actuator in combination with a service brake actuator. The service brake actuator comprises a housing that is divided into a pressure chamber and a pushrod chamber in which is disposed one portion of a pushrod assembly.
The pushrod assembly includes a pressure plate mounted on one end of the pushrod and adapted to abut the diaphragm. A clevis is mounted to the other end of the pushrod and is adapted to connect to a brake lever. The reciprocation of the pushrod with respect to the housing moves the brake lever to apply or release the brakes, depending on the direction of movement. Pressurized air is introduced into the service brake pressure chamber to move the position of the diaphragm and thereby reciprocate the pushrod assembly, resulting in the application or release of the brake, depending on the amount of air introduced or exhausted from the service brake pressure chamber.
The spring brake actuator has a similar construction to that of the service brake actuator in that it typically includes a diaphragm dividing the spring brake actuator into a spring chamber and a pressure chamber. A large force compression spring is housed within the spring chamber between the housing and the diaphragm and is typically separated from the diaphragm by a pressure plate in abutting relationship with the diaphragm. An actuating rod extends from the pressure plate through the diaphragm and into the service brake pressure chamber. The introduction of compressed air into the spring brake pressure chamber compresses the spring and withdraws the actuator from contact with the service brake diaphragm. When it is desired to apply the parking brakes or the emergency brakes, the pressurized air is exhausted from the spring brake pressure chamber whereby the large force compression spring expands, bringing the actuator into contact with the diaphragm to extend the pushrod from the service brake actuator and apply the brakes.
In prior service brake actuators, such as that disclosed in U.S. Pat. No. 5,002,164, issued Mar. 26, 1991, which is incorporated by reference, the pushrod and the clevis of the pushrod assembly are typically assembled after the pushrod has been inserted through an opening in the service brake actuator housing by threading a tapped opening of the clevis onto a threaded end of the pushrod and fixing the relative position of the clevis and pushrod by one or more lock nuts or the clevis was welded to pushrod end. A bushing encircled the pushrod and sealed the pushrod relative to the housing opening through which the pushrod reciprocated. The bushing included a body sized to fit within the service brake opening and a flange sized to abut the service brake housing. A pushrod opening extended through the body. The return spring bore against the bushing to bias the bushing against the service brake housing.
In the prior art, the clevis could not be mounted onto the end of the pushrod prior to the insertion of the pushrod through the housing because the clevis is too large to pass through pushrod opening in the bushing, although it is small enough to pass through the housing opening.
Given the high volume and great price competitiveness of the air-operated brake actuator marketplace, there is a continuous desire to simplify the manufacture and assembly of the air-operated brake actuators. To that end, there is a desire to manufacture and/or assemble the pushrod assembly into a unitary element prior to installation of the pushrod assembly, preventing the use of the current bushing.
The invention relates to an air-operated brake actuator for applying and releasing a brake comprising a housing having first and second portion portions between which is positioned a diaphragm, dividing the interior of the housing into a pushrod chamber and a pressure chamber. The housing second portion has a pushrod opening that extends between the pushrod chamber and the exterior of the housing. A pushrod comprising a shaft having first and second ends, a pressure plate mounted on the first end of the shaft, and a coupling mounted on the second end of the shaft, is mounted within the pushrod chamber such that the pressure plate lies within the pressure chamber, the shaft extends through the pushrod opening, and the coupling is located exteriorly of the second portion. The coupling has a maximum dimension sized to permit passage through the pushrod opening. A bushing encircles the shaft and is positioned within the pushrod opening. The bushing comprises a body sized to be received within the pushrod opening and a shaft opening in the body for receiving the shaft. The bushing has at least one separable portion that enables radial access to the shaft opening, thereby permitting the assembly of the bushing to the shaft after the clevis and pressure plate are mounted to the shaft.
Preferably, the shaft opening maximum dimension is sized to prohibit the passage of the coupling therethrough. The bushing can comprise two arcuate portions which when assembled form the body with an outer circumferential portion received within the pushrod opening and an inner circumferential portion forming the shaft opening. Each arcuate portion can terminate in opposing end portions, with one end portion having a key and the other end portion having a keyhole sized to receive the key to couple together the arcuate portions. The arcuate portions can further include a flange extending beyond the body and which abuts the interior of the housing second portion when the body is received within the pushrod opening.
In another aspect, the invention relates to a method of assembling an air operated brake actuator comprising a housing having an first portion and a second portion, with a pushrod opening in the second portion. A diaphragm spans the housing dividing the housing into a pushrod chamber and a pressure chamber. A pushrod is partially received within the pushrod chamber. The pushrod comprises a shaft, a pressure plate mounted on one end of the shaft, and a coupling mounted on another end of the shaft. The coupling has a maximum dimension sized to permit passage through the pushrod opening. A bushing having a body sized to be received within the pushrod opening and a shaft opening in the body. The bushing comprises at least one portion that is separable from the bushing a sufficient amount to permit the radial insertion of the shaft into the shaft opening.
The method comprising the steps inserting the coupling through the pushrod opening, separating the seperable portion from the bushing to form a radial passage to the pushrod opening, inserting the shaft into the shaft opening through the radial opening, positioning the body in the actuator opening, positioning the diaphragm between the first and second housing portions, and securing the first and second housing portions together.
Preferably, the step of inserting of the shaft into the shaft opening precedes the insertion of the coupling through the pushrod opening. The separable portion is then assembled to the body. The assembly of the separable body portion includes inserting a key on each of the parts into a corresponding keyhole on another part.